The present invention is directed at an improved asphaltic composition and a method of manufacturing same. More specificially, the present invention is directed at an asphaltic composition having improved temperature susceptibility by the addition to the asphalt of certain salts.
Asphalt is a bituminous material generally comprising the bottoms from distillation processes, particularly atmospheric distillations. The atmospheric boiling point of asphalt generally is 400+.degree. C. Because of its good hydrophobic and adhesive properties, asphalt is utilized as a binder in paving materials and as a saturant and coating in roofing shingles. However, before the asphalt can be used in shingles, the asphalt must be further processed to minimize its sensitivity to temperature changes. Without treatment the asphalt may be unacceptably brittle in winter and unacceptably soft in summer. The temperature susceptibility of asphalt has been improved by oxidizing the asphalt. The addition of about 2 weight percent of a mineral acid, such as phosphoric acid, decreases the oxidation time and permits the use of heavier, lower cost feedstocks. U.S. Pat. No. 2,762,755; British Pat. No. 916,531; and U.S. Pat. No. 3,258,419 all are directed at asphaltic compositions which are air blown and/or to which phosphoric acid has been added.
Frequently, a filler material, such as calcium carbonate, is added to the asphalt to decrease the cost of asphaltic compounds and to improve their durability. Addition of a filler is well-known in the art and is discussed in detail in Karchma L. C., Bituminous Materials: Asphalts, Tars, and Pitches, Chapter 28, Vol. II, Part 1, Interscience Publishers New York (1965) the disclosure of which is incorporated herein by reference.
However, it has been found that the addition of calcium carbonate adversely affects the temperature susceptibility of the phosphoric acid-modified asphalt. When calcium carbonate is added, the asphalt becomes softer and flows at unacceptably low temperatures. Shingles manufactured from such an asphaltic composition would be susceptible to blistering and sliding of the coating layer in service.
Accordingly, it would be desirable to provide a phosphoric acid-treated, asphalt calcium carbonate composition having improved temperature susceptibility.
It also would be desirable to provide an asphaltic composition having improved temperature susceptibility in which the improvement in temperature susceptibility is achieved at a relatively low cost and without the use of additional processing equipment.
It also would be desirable to provide a method for improving the temperature susceptibility of asphaltic compounds without unduly increasing the processing time of the asphalt.
The present invention is directed at an asphaltic composition having improved temperature susceptibility and a method for producing same by the addition to the asphalt of a sulfate of a Group IA or Group IIB, preferably selected from the group consisting of sodium sulfate, zinc sulfate and mixtures thereof.